1. Field of the Invention
This invention relates to novel waterglass compositions and to fire resistant glass laminates comprising an intumescent layer between two opposed panes of glass which layer may be produced by drying a waterglass composition on the surface of the glass.
2. Discussion of Related Art
Glass laminates incorporating an intumescent inorganic silicate layer sandwiched between two opposed panes of glass are sold under the trade marks PYROSTOP and PYRODUR by the Pilkington group of companies. When such laminates are exposed to a fire the inorganic layer intumesces and expands to form a foam. The foam provides a thermally insulating layer which protects the pane of glass remote from the fire so that the structural integrity of the glass unit is maintained and thereby presents a barrier to the propagation of the fire for a longer period. The insulating properties of the foam layer also reduce the amount of heat transmitted through the laminate and thereby reduce the risk of combustion of materials on the non-fire side of the glass. Glass laminates incorporating such intumescent layers have been successfully used as fire resistant glass structures. Such laminates may comprise more than two panes of glass sandwiching more than one intumescent layer. Laminates comprising up to eight intumescent layers have been employed. These multi-layered laminates are relatively thick and correspondingly expensive.
The intumescent inorganic layer is normally formed mainly from a sodium silicate waterglass or a mixture thereof with a potassium silicate waterglass. In addition the layer may comprise a minor quantity of a polyhydric organic compound such as a glycol, glycerine or its derivatives or a sugar. The intumescent inorganic layer is most commonly formed by preparing a solution of the waterglass, spreading that solution on the surface of the glass and drying excess water from the solution so as to form the inorganic layer.
U.S. Pat. No. 5,766,770 describes fire resistant glass structures based upon an interlayer formed from a mixture of a sodium silicate waterglass and a potassium silicate waterglass. This disclosure also teaches that it would be advantageous to introduce a minimum of 5% by weight of sub-microscopic particles of an inorganic compound or a metallo organic compound of silicon, aluminium, titanium or zirconium into the intumescent layer in order to increase the viscosity thereof on foaming. The introduction of any particulate material into the waterglass layer is not desirable since the interlayer formed when the waterglass is dried may be hazy or become hazy during the lifetime of the glazing and such glazings are not commercially acceptable.
U.S. Pat. No. 5,766,770 mentions the idea of introducing a metallo organic compound of silicon, aluminium, titanium or zirconium into the waterglass layer but does not disclose any composition containing such a metallo organic compound. To be useful in such a composition the metallo organic compound must be compatible with the waterglass. Many metallo organic compounds are wholly incompatible with the waterglass. One example is zirconium acetate which forms an insoluble white precipitate which is believed to comprise oligomeric zirconium oxide species when added to a waterglass solution. There has no prior disclosure of a waterglass solution comprising a zirconium compound or the use of such a solution to form a fire resistant interlayer.